The purpose of this supplement is to add tau PET imaging with T807 (Avid Radiopharmaceuticals) to all subjects in the Mayo Clinic Study of Aging (MCSA) who participate in imaging (approximately 1,250 based on current response rates). Tau PET is a transformational new technology that for the first time enables in vivo imaging of tauopathy. The MCSA (U01 AG06786) is a population-based study of cognitive aging that was established in Olmsted County, MN in 2004 and was recently renewed for a new 5 year cycle beginning on September 1, 2014. Imaging plays a central role in this latest cycle of the MCSA. This supplement will allow us to determine in vivo tau measures and topography as a function of age from 30 to 90+ years. Cortical tauopathy is found in a significant proportion of autopsy specimens from early adulthood onward. Many key research questions in the field revolve around the staging and progression of tauopathy in relation to contemporaneous clinical findings and findings on other imaging modalities. Elucidating these relationships is critical to understanding the biological underpinnings of typical aging and dementia; to formulating and operationalizing new diagnostic criteria; and, to designing and conducting clinical trials. Key strengths of our application include the population-based design; our findings are therefore not biased by the referral of subjects to specialist clinics or by volunteering. Addition of tau PET to the MCSA through this supplement will enable us to study tau topography in an extremely large number of individuals who will undergo a full complement of state-of-the-art imaging including amyloid, and FDG PET and multi-modal MRI that can be correlated with well- characterized cross-sectional and longitudinal cognitive findings. Our specific aims are: Aim 1: To characterize tau PET findings, develop and validate a method for quantification. Aim 2: Estimate the age- and sex-specific prevalence's of tau PET Braak stages in a population- based cohort age 30-90+ years. Aim 3: Determine cross-sectional topographic associations between tau PET uptake and other biomarkers of AD and cognition. Aim 4: Assess associations between tau PET at baseline and longitudinal cognitive change. Aim 5: To add tau PET to the MCSA protocol in order to provide subjects with state-of-the-art AD biomarker characterization for related research projects.